The present invention relates in general to magnetic disk units that include a magnetic head for reading and writing information on a magnetic disk. More specifically, the invention relates to improvements in a voice coil motor that is used to rotate the magnetic head of the magnetic disk unit
A sectional view of a conventional voice coil motor is illustrated in FIG. 8. The voice coil motor includes a coil disposed on the side of a magnetic head (not shown) parallel to a pair of case bodies 2a, 2b. A pair of upper and lower yokes 4a, 4b, with the coil 3 located between them, are mounted parallel to the case bodies 2a, 2b. Post yokes 5 are provided to form magnetic paths through the upper yoke 4a and the lower yoke 4b and magnets 7a, 7b, 7c, 7d with a cross flux 6 for the coil 3. The magnetic head can be rotated according to Fleming's rule when the coil 3 is activated.
In recent years, there has been a demand to speed up the seek time required to rotate the magnetic head. The seek time could be increased by increasing the thickness of the magnets 7a, 7b, 7c, 7d to obtain a higher flux density in order to improve the output of the voice coil motor. In addition, the thickness of the post yokes 5 could be increased to reduce the degree of magnetic saturation. Increasing the thickness of the magnets or the yokes, however, runs contrary to efforts to maintain a low profile for the magnetic disk unit which is also desirable.
It is therefore an object of the present invention to provide a magnetic disk unit having a faster seek time to rotate the magnetic head while maintaining a low profile in order to achieve an overall thinner magnetic disk unit.